Variable stroke pump



R. J. IFIELD VARIABLE STROKE PUE? 2 Sheets-Sheet 1.

Filed neo. 29, 1944 mg f uv. 3,0, E948.

R. J, IFHELD wyuumsm: STROKE PUMP 2 sheets-sheet 2 Filed Deo. 29, 1941;

Patented Nov. '3 0, 1948 VARIABLE STROKE PUMP Richard Joseph Ield, Ealing, London, England,- assignor to Joseph Lucas Limited, Birmingham,

England Application December 29, 1944, Serial No. 570,439 In Great Britain July 12, 1943 v 1 claim. (ctms-162) This invention relates to variable stroke pumps of the swash plate type, and has for its object to provide improved means for automatically varying the stroke in response to uid pressure.

In the accompanying sheets of explanatory drawings:

Figure 1 is a sectional side elevation, Figure 2 a -part sectional plan, and Figure 3 a sectional end elevation, of a variable stroke .pump of the swash-plate type embodying the invention, Figure 1 being taken on the line I-l of Figure 2, and Figure '3 being taken on the line 3-3 of Figure 1.

The pump shown in the drawings comprises a rotary cylinder block a arranged in a casing b and having formed around its axis a plurality of bores as cin each of which is arranged a reciprocatory plunger d. The outer ends of the plungers d abut against a swash plate e which is pivotally supported in the casing b by trunnions f, and is movable about its pivot axis for altering the stroke of the plungers. During rotation of the ,cylinder block a thefplungers d are moved in one direction by the swash plate e and in the opposite direction by springs as' g, the latter being situated within the bores c, and serving to hold an i' end face of the cylinder block in contact with a flat seating h in the casing b. The seating h is formed with a port i communicating with the pump inlet i, and with another port k communieating with the pump outlet m, the pump inlet and outlet being provided in opposite sides or one end of the casing b.

In applying the invention in the manner.

shown in the drawings to the pump above described, I mount in bores n in the casing b a pair of controlling plungers o, p for imparting opposite angular movements to the swash plate e, the plungers being adapted to act on the swash plate at opposite sidesI of its pivot axis. At the end of the controlling plunger o remote from the swash plate e there is formed in the casing b a chamber q, and in this chamber is arranged a spring r which acts on the plunger through the medium of a thrust piece s, and which is adapted tomove the plunger and swash plate in the direction for increasing the stroke of ythe pump plungers d. When the pump is required to operate under high delivery pressure I preferably arrange that the chamber q shall also communicateA by a passage t with the pump outlet m. The

.pressure-to which the plunger o is then subjected is the sum of the spring and delivery fluid pressures. For convenience of manufacture and to enable the pump to operate in either direction of rotation, the chamber q may also be connected by another passage u to the pump inlet 7', this passage being closed by a removable non-return valve 1J or a plug. At the corresponding end of the other controlling plunger p there is formed in the casing b a cylindrical chamber w containing a piston :c formed on or otherwise associated with the plunger and of appropriately larger -diameter than the plunger, the latter serving to move the swash plate e (under the action of fluid pressure on the piston) in the direction for reducing the stroke of the pump plungers d. The chamber w is adapted to communicate with the pump inlet i and outlet m under the automatic control of a piston valve y which is loaded by an adjustablespring z.` To accommodate the valve y the casing b is formed with a transverse bore 2, and in the centre of this bore is secured a coaxial bush 3 in which the valve is slidably mounted. The parts of the bore 2 situated at opposite ends of the bush 3 are respectively connected to the pump inlet 7 and outlet m by passages t, 5 in the casing b. Also the bush 3 is provided with ports t which serve under the control of the valve y to control communication of the pump inlet and outlet m with another passage i formed in the casing e and leading to the cham'- ber w.

The pressure acting on the controlling plungr p having the piston a: associated with it depends on i the position of the piston valve y. At low pump delivery pressures, the valve y is in the position shown in Figure 3 in which it effects communication of the piston chamber w with the pump inlet gi. But when a predetermined pump delivery pressure is exceeded this pressure moves the valve y in opposition to its spring e into a position in which it establishes communication between the pump outlet m and the piston chamber w. The fluid pressure now acting on the piston a.' moves the swash plate e in the direction for reducing the pump plunger'stroke, and this motion is vcontinued until a state of balance is` reached.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

A variable stroke pump comprising in comlbination a casing, a rotary cylinder block of the plungers in one direction, an outlet through are alternatively connectible to the said chamber v under the control of the valve.

RICHARD JOSEPH REFERENCES CITED The following references are of record 1n the le of this patent:

UNITED STATES PATENTS Number Name Date Re. 21.758 Foisy Apr., 1, 1941 2,129,886 Syrovy Sept. I3, 1938 2,177,098 Doe et al Oct. 24, 1939 2,292,125 Ield Aug. 4, 1942 2,299,285 Snader et al Oct. 20, 1942 

